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Thread: Air Conditioning Oil: When and How Much?

  1. #1
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    Air Conditioning Oil: When and How Much?

    I have replaced the condenser and the drier, but not the compressor. I have no idea if the compressor was ever replaced. Do I need to add oil before I recharge the system. If yes, how much and is PAG 46 the correct oil?

  2. #2
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    It requires 160ml (5.4 oz) of PAG oil - but I would recommend having the system evacuated by one of those automatic machines to check for vacuum hold - which also helps to boil off the moisture that will have accumulated in the drier as the system has been open for a month or so!
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  3. #3
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    Quote Originally Posted by Timm View Post
    It requires 160ml (5.4 oz) of PAG oil - but I would recommend having the system evacuated by one of those automatic machines to check for vacuum hold - which also helps to boil off the moisture that will have accumulated in the drier as the system has been open for a month or so!
    Thanks Timm. After evacuating the system will the compressor still have oil in it. Is it possible to add too much oil and thus, ruin the compressor?

  4. #4
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    The automatic machines get everything out - recycles what it can and then recharges the system with the correct amount of PAG oil and refrigerant....
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  5. #5
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    Quote Originally Posted by Timm View Post
    The automatic machines get everything out - recycles what it can and then recharges the system with the correct amount of PAG oil and refrigerant....
    I already started to charge the system and I reached the point of equilibrium. There are two switches on the drier, one white and one black. Which do I need to shunt to get the compressor to turn on to pull refrigerant into the system.

  6. #6
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    There should be no need to short any contacts - when filling from the LOW PRESSURE connector, as soon as the refrigerant pressure reaches 1.6 Bar (21 psi) the compressor should kick in. More info here:

    https://www.meeknet.co.uk/e31/E31_Regas.htm

    Give us some idea on how you are trying to ragas the system.....
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  7. #7
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    Quote Originally Posted by Timm View Post
    There should be no need to short any contacts - when filling from the LOW PRESSURE connector, as soon as the refrigerant pressure reaches 1.6 Bar (21 psi) the compressor should kick in. More info here:

    https://www.meeknet.co.uk/e31/E31_Regas.htm

    Give us some idea on how you are trying to ragas the system.....
    With a gauge set I ran a vacuum pump for an hour with low and high side open. I then closed the low and high side and waited an hour. No leaks, the system maintained vacuum. I then connected a can of refrigerant to the low side and opened the low and high side and opened the refrigerant valve with the engine off. I got to 3lbs on the low side and 0 on the high side. I closed the low side and high side and closed the valve on the refrigerant can. I then turned on the engine and the ac on max, and I opened the low side and the valve on the can of refrigerant. I did not open the high side. The compressor would not turn on. Before I replaced the condenser and drier the compressor worked fine. I sprung a leak in the condenser and lost all the refrigerant which started this process of repair. I do not want to return to a shop because one has already caused me grief and I have no recommendations for another shop I can trust to do this right. BMW down here is a rip off, so they are a last resort if I cannot resolve this.

  8. #8
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    Nothing is going to happen at 3 psi - you need to reach 21 psi at the very least before the compressor will kick-in. Follow the link and you will get there:

    https://www.meeknet.co.uk/e31/E31_Regas.htm

    Filling a system with cans is a bit expensive as the system takes 1.5 Kg - which is why I recommended the automatic machines - the operator is guided through the whole process and the connectors only fit one way around so they can't make mistakes (easily).
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  9. #9
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    Bumping this thread since it has good info and I've got a question. 98 740 that's had the engine replaced at the dealership like 11yrs ago, long story but the car sat for like 10yrs and I don't recall why but the AC never got recharged.

    Fast forward to today and my buddy's shop bought a Mehle Arctic Cool AC setup. We recharged the AC today, it's running nice and stone cold, added nearly 3lbs of refrigerant but our question is about PAG oil. We have no idea if there was ANY oil left in the system so he decided to add only .5oz of oil. His machine also has PAG 46 but I've read the car might need 100 instead? Either way, it's stone cold as I've driven about 20 min and still cold as I'm idling and writing this.

    My concern is how much oil may have resided in the system, if PAG 46 is fine and if we need to redo it all over again for more oil and/or a different oil.
    Last edited by m5james; 09-03-2022 at 05:49 AM.
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  10. #10
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  11. #11
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    Quote Originally Posted by m5james View Post
    ...We have no idea if there was ANY oil left in the system...
    On yet another vehicle (not e31, not e38), I'm at that same point with the same question(s).
    Background: I've been doing my own AC for years, have my own pump and gauges, have general knowledge of everything but not a tradesman, not a factory engineering, not a lawyer.

    Two observations / intuitions / opinions in regards to oil quantity ...

    * It's an unknowable unknown.

    I went around my system (compressor, drier, condenser, etc) measuring oil, auditing for 134 green o-rings.

    Consider my condenser...
    Took it off the vehicle, turned it this way and that. Nothing.
    Then I attack it with compressed air and blew out perhaps 1oz of oil.
    Oil was in there, and would be unless the condenser was spanking new.
    There were two mysteries: 134 compatible? and how much did not get blown out?

    Point is...Oil will hide in pockets throughout the system and you will never have a full accounting of the quantity.
    A fanatical inquisition would tally only a rough estimate.
    So...how can precision be important yet no one (service shop personnel) could ever know the precise answer?


    * Factory specs imply a precision that is not necessarily intended.

    This is a frequent hazard in engineering & management when a number MUST be listed, but the actual value is quite arbitrary within a wide range of acceptable.
    As an example I brought in a NEW compressor wrapped in oem factory documentation.
    The unit is a Nippon Denso and ships against a number of systems (vehicle applications), not tailored or adjusted to any one in particular.
    The oem docs lists a number and range similar to what's listed for ND in the BMW docs, and I will assume BMW merely propagated oem numbers.
    However, the oem doc also says...

    "We've shipped this compressor with a lot of oil (4oz per my measurement, consistent with docs) and you the installer should reduce it down to whatever your last compressor had."
    {ed: By comparison the outbound compressor had <1oz oil. Big difference. Am I to believe that is somehow correct and a target number?}

    So... although the oem factory lists a number, they seem to consider oil quantity to be a soft number, not listing their minimal number for their compressor unit, only system total, independent of application (size) AND they imply that they ship overfilled. Seems a bit sloppy to me, not precise and controlled at all. The final result is ultimately passed off to the service people, and hence back to problem 1.

    So...IMHO, in automotive HVAC systems 1) it doesn't take much to keep machinery lube'd and seals sealed and 2) there is no requirement of heat extraction or dissipation as with engine oil,
    ...and therefore it's OK to bias towards "less" or minimal, and not fret over the exact amount.
    Last edited by Hyper; 09-03-2022 at 11:01 AM.

  12. #12
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    As far as I understood - the way to measure and remove oil from a refrigerant system was to place it in a deep vacuum - at which point any liquid becomes a gas and is extracted. That is why the automatic machines can remove moisture and measure (and remove) any oil in the system, and at the same time check for a drop in vacuum indicating a leak. Once measured it can recycle the pag oil and refrigerant....
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  13. #13
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    Water boils off, the oil stays behind.
    Something about vapor pressure.
    As a logical confirmation, my Robinair vac pump exhausts to the atmosphere and yet my shop does not fill up with oil.
    ***
    I'm not familiar with auto machines, could be that they are somehow measuring saturation of the refrigerant (like this sample contains 0.01% oil or whatever).
    This would be useful as it would be measuring a system metric, of the system being serviced.

  14. #14
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    Crap shoot it is lol. Either way it's running great and nowadays M62's are pretty common at junkyards so it'll be a cheap replacement if the pump shits the bed.
    650hp 10 X5///M5
    PERFORMANCE:JB4 w/ meth, stage 2 tune, wrapped downpipes, custom intake
    INTERIOR:AVIN 10.25" screen, Blackvue 550 dashcam, 7" tablet for JB4 logging
    EXTERIOR:Niche staggered 20's or AC Forged staggered 22's, H&R 2" suspension, LED AE, CF front splitter
    325hp 98 BMW 740iL6
    PERFORMANCE:///M5 6spd swap, iron sleeves, L/W Teflon coated & silicone impregnated pistons, Sealed Power rings, 3 angle valvejob, P&P head, perf cams, electric fan, CF intake tube w/aluminium heatshield/wrapped MAF tubing, Magnaflow 14816'd, Eaton M112 in-work
    INTERIOR:Android Dynavin, hardwired V1 above rearview, 12" RE Audio DVC sub, MTX 81000D monoblock, CF silver trim, 5% tint
    EXTERIOR:///MPar staggered 19's, H&R Stage 2/Bilstein HD, custom notched bumper, Shadowline trim, 750iL brakes w/ Axxis pads
    190hp 97 328ci
    PERFORMANCE:Single mass flywheel, ///M3 clutch
    EXTERIOR:Z4///M staggered 18's, rolled fenders, tinted markers

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